Abstract

For the first time, the quasiperiodic Bragg fibers with geometrically distributed multilayered cladding are proposed and analyzed. We demonstrate that hollow-core Bragg fibers with quasiperiodic dielectric multilayer cladding can achieve low loss transmission over a broadband wavelength range of more than an octave (from 0.81 μm to 1.7 μm). The periods of the Bragg blocks follows a geometrical progression with a common ratio r<rc, where rc is defined as the critical ratio of the periods of two adjacent Bragg blocks. The arrangement of the quasiperiodic cladding can significantly modify the characteristics of the fiber, leading to a broadening of the guiding range compared to a hollow Bragg fiber with uniform periodic multilayer cladding structure. In general, a larger r value results in a broader guiding range. More Bragg blocks in the cladding and more unit cells in each Bragg block lead to a lower fiber modal loss.

Figures (10)

(a) Schematic diagram of the hollow-core Bragg fiber cross-section. (b) The quasiperiodic cladding is formed by m numbers of Bragg blocks; there are N unit cells in each block, i.e. N pairs of two dielectric materials alternating in the block. The period for k-th Bragg block is pk. The ratio of the periods in two adjacent Bragg block is r = pk/ pk-1. (c) An example of a quasiperiodic Bragg fiber with m = 2, N = 4, r = 1.5, and (d) its refractive index profile in radial direction.

Projected band structure of the planar periodic multilayer structure. The refractive index of the two materials in the Bragg cladding nL = 1.625, nH = 2.896. The solid line is the light line. The gray and black regions correspond to TE allowed band, and TM allowed band respectively. The white regions correspond to the total bandgaps.

(a) The bandedge wavelengths of the fundamental bandgap for the periodic 1D PC (upper), and the quasiperiodic 1D PC (lower). There is obvious broadening in omni-reflection range marked by the solid-dash lines. (b) The transmission at incidence angle θ=90° for TE (dashed) and TM (solid) polarizations.

Loss of TE01 mode of the periodic (solid curve) and quasiperiodic Bragg fiber (solid curve with circles). (a) The Bragg cladding has the following parameters: nL, nH are from [13], m = 5, N = 6, the periodic Bragg fiber has 1D PC, p1=p2=⋅⋅⋅=pm=287nm. The quasiperiodic Bragg fiber has hetero-structured cladding, p1=287 nm, pm/p1=1.2. (b) The cladding materials are SiO2/As2Se3, the fiber structural parameters are the same as those used in Fig. 9(a) with cladding materials of PES/As2Se3. The Loss of TE01 mode of the quasiperiodic Bragg fiber shows an evident broadening with pm/p1varying from 1.0 (solid star line) to 1.2 (solid square line).